Dental posts are used in reconstruction of endodontically treated teeth. The function of the dental post is to provide retention and lateral stability to the restoration. The restorative material is used to build the core and the crown at the coronal end of the tooth. In order to provide effective lateral stability, the dental post should have high stiffness in the coronal region. Stiffness refers to Young's modulus, which is the resistance of a material to deformation. Another important function of the dental post is to disperse occlusal forces from the coronal region to the remaining tooth structure. In addition, a good dental post should have a long fatigue life and high corrosion resistance.
In view of the above-stated requirements, state-of-the-art dental posts are either made of stainless steel, titanium or other metal alloys, or fiber reinforced composites, which have stiffness much higher than that of dentine, Although, the high stiffness is generally recognized as being necessary for the effective support of the restorative material in the coronal region of the tooth in order to prevent loosening of core and crown, it also gives the major drawback of causing stress concentration at the apical end of the tooth. The rigid post stiffens the coronal posted section and shifts the flexure point apically. The effect of this stiffening is to cause the non-posted apical portion of the tooth to deform at the post apex, resulting in a stress increase in that portion of the canal wall. Furthermore, the cyclic loading and unloading during mastication requires consideration of fatigue failure. Since the maximum bending stresses occur in the vicinity of the apex of the post, any inclusions or defects within the wall of the dentine near the apical end of the post would create stress concentration that increases the risk of a fatigue crack formation. Defects and microfractures introduced during endodontic treatment and post access preparation could become areas contributing to stress concentration. As a result, fractures frequently occur at the root of the tooth. Furthermore, the high stress experienced at the post-dentine interface of a high stiffness post often causes loosening at the post-dentine interface.
Various designs have been suggested in the art to address some problems stated above. These include tapered posts (U.S. Pat. No. 5,104,321), and flexible posts (U.S. Pat. No. 5,518,399). For tapered posts, the change in the shape of the post affects the bending stiffness without changing the Young's modulus of the post. Since Young's modulus is a critical parameter in determining the stress loading at the post-dentine interface, a tapered post does not solve the problem of root stress resulting from the high stiffness of the post. Furthermore, wedging effect occurs at the tip of the tapered end, resulting in vertical fractures. A flexible post has a reduced Young's modulus, which reduces the problem of root stress, but may not give sufficient support to the restoration, resulting in loosening and early failure of the restoration.